AUSTIN/DALLAS, Texas (Reuters) - Women seeking to terminate their pregnancies were turned away at clinics across Texas on Friday, providers said, after strict new regulations for physicians who perform abortions prompted a dozen facilities to stop offering them.

Facilities that continue to perform abortions were flooded with calls from women trying to find alternatives, clinic officials said.

"They're calling from all over - Fort Worth, West Texas, all over Dallas, Oklahoma, everywhere," said Betty Pettigrew, director at Routh Street Women's Clinic in downtown Dallas, which has offered abortion services since 1978.

Offices were inundated with calls after a federal appeals court ruled on Thursday that a provision of a new Texas law that requires all doctors performing abortions to have an agreement with a local hospital to admit patients could go into immediate effect.

The provision was part of a sweeping anti-abortion law, passed in July by the Republican-led Texas Legislature, that also requires abortion clinics to meet heightened building standards, bans abortion after 20 weeks and requires strict adherence to federal guidelines in prescribing the so-called abortion pill.

Hours after the decision from the U.S. Fifth Circuit Court of Appeals, managers or employees of 12 clinics from El Paso to Dallas to the Rio Grande Valley said their facilities would either drastically reduce the number of procedures, or stop providing abortions altogether.

Opponents had warned before the court decision that abortion services at nearly one-third of the state's 32 clinics and an additional half dozen ambulatory centers that also offer the procedure could immediately halt as soon as the law went into effect because many doctors have not been able to gain admitting privileges.

"Unfortunately, we are having to close today and tomorrow, but we will be open next week seeing patients as normal," said Tenesha Duncan, administrator at Southwestern Women's Surgery Center in Dallas. The doctor on duty Friday and Saturday does not have admitting privileges, she said.

Anti-abortion groups who support that law questioned why some clinics had been able to meet the new requirements and not others. They said the requirement that doctors performing abortions have admitting privileges was enacted to enhance safety for women.

"We have to make sure that abortions are done in a manner which is consistent with accepted safety standards," said Joe Pojmann of the Texas Alliance for Life in Austin.

Some 45 women were denied their previously scheduled abortions at Whole Woman's Health clinics in Fort Worth, San Antonio and McAllen, Texas, on Friday, said Amy Hagstrom Miller, chief executive officer and founder of Whole Woman's Health, which operates four clinics and one ambulatory surgery center in Texas.

"They were all in tears," Miller said. Some of Whole Woman's clinics are open for now because they still must do required follow-up appointments for women who have already had abortions.

Two of that network's facilities will have to shut down completely in a matter of weeks - staff let go, buildings sold - if they cannot gain admitting privileges because abortions comprise 90 percent of their services and the company cannot afford to run those offices without that revenue, Miller said.

"We specialize in abortion care because in most communities, there are plenty of family planning and ob-gyn services, and it's really abortion care that's underserved," she said.

The group's clinic in San Antonio, which is currently open five days a week, will have to reduce its hours to once or twice a month because the only physician with admitting privileges at that facility lives on the East Coast and is flown in for procedures, Miller said.

Harlingen Reproductive Services in South Texas halted abortions but remained open for other women's health services, said Angie Tristan, clinic administrator said.

At Reproductive Services in El Paso, officials are hopeful that they can soon gain admitting privileges for its physician.

"We hope to be back up and running with abortion services next week," administrator Gerri Laster told Reuters.

Some of the clinics that are closing or discontinuing the procedure may resume if their doctors can gain admitting privileges, clinic officials cautioned, though many hospitals are reluctant to do so for religious or business reasons.

No clinic had reported any official closings to the Texas Department of State Health Services, which tracks licensed abortion facilities, by Friday, said agency spokeswoman Carrie Williams.